Electrical oscillator apparatus for medical purposes



Sept. 1, 1942, w, AY 2,294,411

ELECTRICAL OSCIiJLATOR APPARATUS FOR MEDICAL PURPOSES Filed Sept. 21, 1938 Ourmq' [Lia rpapis L c 1 FIT/18E C9 f V 8 1;

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INVENTORV ARTHUR WILLM LAY ATTORNEY I Patented Sept. 1,1942

ELECTRICAL OSCILLATOR APPARATUS FOR MEDICAL rUnrosEs Arthur William Lay, Chelmstord, England,'as-

poration of Delaware aignor to Radio Corporation of America, a cor- Application September 21, 1938, Serial'No. 230,898 in Great Britain October 5, 1937 5 Claims.

This invention relates to electrical oscillator apparatus for medical purposes and more particularly to such apparatus-oi the type sometimes referred tp under the term Faradic' interrupter. The invention provides improved apparatus suitable for use for the various medical purposes for which shocking coils are at present commonly used.

According to this invention an electro-medical oscillator apparatus comprises an oscillator circult of the relaxation oscillator type, an oscillator valve circuit so arranged that normally, 1. e. in the absence input thereto, self-oscillation does not occur, means for applying impulses from the relaxation osclllator circuit to of said valve circuit so as to cause said valve circuit to burst into. oscillation upon the application of an impulse thereto, the generated oscillations thereafter dying away, and a patients output circuit fed from the'output of the valve circuit. l -i..

The invention is illustrated in the accompanying diagrammatic drawing, 3,;

Figure 1 shows diagrammatically a"cii cuit arrangement having a high frequency;;oscillator, controlled by a low frequency relaxation oscillator, and l Fig. 2 shows an alternative circuit arrangement in which both the high frequency oscillator and low frequency relaxation oscillator are also used.

Referring to Figure 1 which shows one arrangement in accordance with this invention there is provided a neon or like discharge tube V3 in series with a fixed resistance R; and an adjustable resistance P2 of source of direct current potential, the anode of the discharge tube being connected to the positive terminal of the source. In shunt across the discharge tube is a fixed condenser, or if desired, and as shown, a plurality of fixed condensers C5, C6, C1 of difierent values may be provided and a switch S associated with said condensers whereby any one of the said condensers may be connected in shunt across the discharge tube. If desired; the switch may be so arranged that it can connect any combination of said condensers across the tube V3. Connected in shunt across the series connected elements R2 P2 is a coupling condenser C8 which should be small relative to high value across a the condensers C5 C6 C1, in series with a po tentiometer resistance Pl an adjustable tapping point upon wh ich is connected to the control grid GI of a valve ,V2 having a plurality of gridsior example, asshown, a tetrode ot the indirectly heated cathode type-whose cathode K is connected to the negative terminal of the potential supply source through a capacity shunted resistance combination C3 RI. The second or screen grid G2 of the tetrode V2 is connected to one end of a parallel tuned circuit consisting 0! a capacity C8 and an iron cored inductance Ll in parallel, the other end of this tuned circuit being connected through a variable reslstance P3 and a condenser C4 to the anode A of the valve. A centre tap CT upon the inductance L! ;is connected to the positive terminal of. the D. C. potential source. The anode A of the valve is also connected to the said positive terminal through the primary L2 of a transthe' input 15 former the secondary L4 of which constitutes the patients output circuit.

It will be seen that this valve circuit is of the well known Hartley type and it is so adjusted that in the absence of input to the first grid Gl the said circuit does not oscillate. When, however, a positive pulse is applied to the first .or control grid G! the valve impedance is lowered s'ufilciently for oscillation to occur and oscillation commences at an amplitude determined ,by that of the pulse supplied, the said oscillations dying away exponentially and ceasing until the-next pulse occurs. The neon or like tube V3 of course forms part of a relaxation oscillation "generator the frequency of which can be adjusted by varying the adjustable resistance P2.

Since .the coupling condenser 08 in series with the potentiometer Pl from which positive pulses are applied to the grid GI of the tetrode V2 is of small value (.01 of a microfarad is a practical value given by way of example) the discharge absorbed is also small and as this is of long period the charging does not substantially influence the wave form. When the neon or like tube V3 is not in operation (i. e. when a discharge is not occurring therein) the condenser or condenser combination in shunt therewith charges up slowly, and its potential rises slowly, the coupling condenser C8 meanwhile discharging through the potentiometer resistance. When the tube V3 reaches its ignition voltage and flashes, thepotential across the condenser or condenser combination in shunt therewith collapses and a positive impulse is applied through the coupling condenser C8 to the first grid of the tetrode.

In the embodiment of the invention shown in Figure 2 the relaxation oscillation generator circuit is connected as in Figure 1 and the patients output circuit is, as before, fed from the secondary L4 or a transformer whose primary. L2

one end of a parallel tuned circuit C9 LI the centre point CT of which is connected to the negative terminal of the D. C. source and the practically eliminated, (2 the apparatus may be operated 01! D. C. or A. C. commercial power lines, (3) the operation is silent, and (4) full and easy control both of frequency and amplitude is obtainable.

As regards advantage (1) the function of the 7 main impulses, i. e. the impulses originating with the potentiometer PI and is also connected to .the relaxation oscillator circuit and the frequency of which is variable is to produce that physioother end of which is connected through an adjustable resistance P3 and a condenser C4 in series, to thesecond or screen grid G2 of the tetrode V2. The said second grid G2 is connected to the positive terminal 'of the D. C.

source through a suitable further resistance R4.

and the cathode K is connected to the negative terminal of the said source through a capacity shunted resistance combination RI C3. If desired a resistance R5 may be connected across the tuned circuit C9 LI as shown. In this modified circuit, therefore, there is a Hartley circuit operating across the two grids GI G2 of the tetrode V2, the oscillations being governed by the control grid GI and the second or screen grid G2 being fed with D. C. potential and also subjected to modulation. The main advantage of this circuit is that it provides a somewhat better constancy of output under varying conditions of loading in the patients circuit.

The above described circuit arrangements are well adapted for mains operation and may be fed from any D. C. source or, as shown in the two figures, through a suitable rectifier network of any known type, from an A. C. mains source. For example, either may be fed from A. C. or D. C. mains as shown. In Figure 1 an A. C. power source feeds through fuses F and an onand-ofi switch MS into a full wave rectifier circuit including a double diode VI with an ordinary series inductance and shunt capacity smoothing filter L3 CI C2 in its D. C. positive output lead. Where the valve V2 is of the indirectly heated cathode type its heater HI may be connected as shown in series with the heater or filament H2 of the rectifier and with a ballast resistance B direct from the power source. The power circuit shown in Figure 2 is almost the same as in Figure 1; a little more elaborate smoothing circuit is, however, shown, the filter comprising two inductances L5 and L3 and three condensers CI C2 CID. In both figures the power supply terminals AC are also marked and to indicate-as will be obviousthat a direct current source may be connected to these terminals if desired.

The amplitude of the positive pulses applied to the first grid GI of the valve V2 may, in either circuit, be controlled by varying the tapping on the potentiometer PI to which said grid is connected and further control as respects the oscillatory condition of the said valve may be obtained by varying the adjustable resistance P3 in either circuit. v

Since in both circuits the patients output circuit is fed through a transformer L2 L4 the patient is isolated from the commercial power source.

Among the numerous advantages of the above described circuits over the well known choking co'il arrangements are (1) painful skin eiiects are logical stimulation which has proved .beneficial for many medicalpurposes. The small damped higher frequency oscillations set up by the valve oscillator circuit serve to' reduce or eliminate painful skin effects which small D. C. currents tend to cause as a result, it is believed, oi rectifying action in the human skin.

A practical range of frequencies for the main impulses is from about 10 to 500 impulses per minute, but this frequency can, of course, be increased, if desired, up to a limit set by the neon or like discharge tube employed.

What is claimed is 1. An electro-medical oscillator apparatus comprising an oscillator circuit of the relaxation oscillator type, an oscillator valve circuit so arranged that normally self-oscillation does not valve circuit is of the Hartley type, the, valve in which has a second grid in addition to the control grid to which the impulses from the relaxation oscillator circuit are applied, and said Hartley oscillatory circuit is connected to operate across the second grid and anode of the valve.

3. Electrical medical oscillator apparatus comprising an electron discharge tube of the tetrode type, a resonant circuit connected between the anode and a grid adjacent the anode of said tube, means including a control grid in said tube for producing a normally non-oscillatory condition in said tube, means including a relaxation oscillator having a time constant device connected thereto and having aconnection to said control grid for periodically initiating oscillations in said tube and for thereafter damping said oscillations, and a utilization circuit coupled to the output circuit of said tube. 4. Apparatus according to claim 3 and having a gas-filled discharge tube in said relaxation oscillator.

5. In a device of the class described, a pmrality of separate discharge devices including a vacuum tube of the tetrode type and a gaseous diode tube, circuit means interconnecting certain electrodes of said tubes in such manner as to produce relaxation oscillations v in the vacuum 

